Method of producing gypsum/fiber board

ABSTRACT

A gypsum/fiber board having improved impact resistance is produced by mixing predetermined amounts of fibers, calcined gypsum and water to form a mixture of wetted, loose fibers; laying out a reinforcing mesh over the upper surface of a forming belt; depositing said mixture on said mesh to form a layer of said mixture, said; and compressing said mesh together with said layer of mixture to embed said mesh in the lower surface of said layer to form a board composed of bonded fibers and gypsum with said mesh embedded in the surface thereof.

This application claims the benefit of U.S. Provisional Application No.:60/099,646 filed Sep. 9, 1998.

BACKGROUND OF THE INVENTION

The present invention relates generally to a paperless gypsum/fiberboard with improved impact resistance and to a process for making such agypsum/fiber board. More particularly, the present invention relates toa multi-layer gypsum/fiber board having a fiberglass mesh embedded inthe backside to provide improved impact resistance.

Conventional gypsum wallboard or panel is typically manufactured from aplaster slurry wherein a wet slurry of calcium sulfate hemihydrate,generally referred to as calcined gypsum, is placed between two layersof paper and the slurry is allowed to set. The set gypsum is a hard andrigid product obtained when the calcined gypsum reacts with water toform calcium sulfate dihydrate. Calcined gypsum is either calciumsulfate hemihydrate (CaSO₄•½H₂O) or calcium sulfate anhydrite (CaSO₄).When calcium sulfate dihydrate is heated sufficiently, in a processcalled calcining, the water of hydration is driven off and there can beformed either calcium sulfate hemihydrate or calcium sulfate anhydrite,depending on the temperature and duration of exposure. When water isadded to the calcined gypsum to cause the gypsum to set, in essence, thecalcined gypsum reacts with water, and the calcined gypsum isrehydrated. In typical gypsum wallboard, the two layers of paper containthe slurry and provide the strength required in installation and use.The wallboard is cut into discrete lengths to accommodate subsequenthandling and then dried in heated dryers until the board is completelydry. The bending strength of the wallboard depends largely on thetensile strength of the paper. The set gypsum serves as the core andaccounts for fire resistance and can be modified for variousapplications. The paper determines the nature of the application for theboard and the surface treatment that may be used on the board.

Although paper-covered wallboard has many uses and has been a popularbuilding material for many years, the prior art has recognized that forcertain applications it would be advantageous to provide a gypsum panelthat did not rely on paper surface sheets for strength and otherproperties. Several prior art fiber-reinforced gypsum panels are asfollows:

U.S. Pat. No. 5,320,677 to Baig, which is incorporated by referenceherein in its entirety, describes a composite product and a process forproducing the product in which a dilute slurry of gypsum particles andcellulosic fibers are heated under pressure to convert the gypsum tocalcium sulfate alpha hemihydrate. The cellulosic fibers have pores orvoids on the surface and the alpha hemihydrate crystals form within, onand around the voids and pores of the cellulosic fibers. The heatedslurry is then dewatered to form a mat, preferably using equipmentsimilar to paper making equipment, and before the slurry cools enough torehydrate the hemihydrate to gypsum, the mat is pressed into a board ofthe desired configuration. The pressed mat is cooled and the hemihydraterehydrates to gypsum to form a dimensionally stable, strong and usefulbuilding board. The board is thereafter trimmed and dried. The processdescribed in U.S. Pat. No. 5,320,677 is distinguishable from the earlierprocesses in that the calcination of the gypsum takes place in thepresence of the cellulosic fibers, while the gypsum is in the form of adilute slurry, so that the slurry wets out the cellulosic fibers,carrying dissolved gypsum into the voids of the fibers, and thecalcining forms acicular calcium sulfate alpha-hemihydrate crystals insitu in and about the voids.

U.S. Pat. No. 5,135,805 to Sellers et al, describes a water resistantgypsum product that may be a “faceless” product, i.e. it may not includea facing sheet of paper, fiberglass mat or similar material. The gypsumproducts described by U.S. Pat. No. 5,135,805 typically containreinforcing fibers, for example, cellulosic fibers, such as wood orpaper fibers, glass fibers or other mineral fibers and polypropylene orother synthetic resinous fibers. The reinforcing fibers can be about 10to about 20 wt. % of the dry composition from which the set gypsumproduct is made. The density of such a product is typicality within therange of about 50 to about 80 pounds per cubic foot.

U.S. Pat. No. 5,342,566 to Schafer et al, which is incorporated byreference herein in its entirety, refers to a method of producing fibergypsum board comprising the steps of mixing in a preliminary mixing steppredetermined amounts of fibers and water respectively, to form amixture of wetted, loose fibers; mixing in a mixing step the wettedfibers with a predetermined amount of dry calcined gypsum; premixing anaccelerator with one of the components of dry calcined gypsum, fiber andwater; promptly laying the mixed composition into a mat; immediatelydegassing the mat in a first compression step, adding a predeterminedamount of water onto the resultant mat; and immediately compressing themat to form a board composed of bonded fibers and gypsum. This processmay be used to produce a homogeneous board which is preferably a gypsumboard reinforced by fiber, such as paper fiber, wherein several layersof board forming materials are placed on each other before the board isfully formed, pressed, and dried and wherein each of the layers isidentical in composition. Schafer et al specifically describes theformation of a three layer board wherein the central, core layer has acomposition which differs from the composition of the outer layers.

Carbo et al Provisional Application Serial No. 60/073,503, describes amulti-layer, paperless gypsum/fiber board and a process for making sucha three layer gypsum/fiber board wherein the central, core layer has acomposition which differs from the composition of the outer layers, allof which is incorporated by reference herein in its entirety.

Prior art gypsum/fiber boards have been modified by adhering a layer ofmesh to the back of the board, in order to provide improved impactresistance. While such modified boards had improved impact resistance,the production rates of such board were low, the energy costs werehigher, the materials cost increased, the labor cost increased, becauseof the need to laminate the gypsum boards to the mesh in separateprocesses that have control problems with respect to the laminationprocess and the problem of blocking between panels. The process oflamination can be difficult with any variation of thickness of the panelbeing covered with a mesh or solid reinforcement. With variation inthickness or profile the lamination process is a problem with respect tomaintaining constant pressure across the panel. The problem of blockingpanels which stick to one another is a significant problem whenlaminating mesh's on surfaces as the glue can actually glue the stackedpanels to one another in addition the mesh on the surface.

It is the object of the present invention to provide a fiber-reinforcedgypsum board that has improved impact resistance that avoids many of theproblems of the prior art gypsum/fiber boards. More particularly, it isthe object of present invention to provide a multi-layer gypsum/fiberboard having a fiberglass mesh embedded in the backside to provideimproved impact resistance as determined by Soft Body Impact Resistanceaccording to ASTM E695 and by Hard Body Impact Resistance according toUSG method as documented in independent reports HPWLI #7122 and HPWLI#7811-02. Embedding a reinforcing mesh to the gypsum/fiber board, inaccordance with the present invention, provides many advantagesincluding high production rates; better product aesthetics, integralconsolidation of reinforcing mesh in board and reduced product cost.Embedding a reinforcing mesh also improves the handling properties ofthe board and reduces the tendency of the board to block (adhere toadjacent boards when horizontally stacked). The product of the presentinvention can include a flush mesh which does not mark up the face ofthe panel on which it is stacked, and improved retention of thereinforcement in the panels as it is protected from wearing and rubbingon the surface. Another product benefit is the tensioning of the mesh inthe product to provide enhanced stiffness to the panel. In terms of theprocess the present invention eliminates the need to transport thepanels to secondary operations, and allows the reinforced panel to beproduced on a standard gypsum fiberboard line.

SUMMARY OF THE INVENTION

The present invention relates generally to a paperless gypsum/fiberboard with improved impact resistance, and to a process for making sucha gypsum/fiber board. The term “paperless” gypsum/fiber board, as usedherein, is intended to distinguish the fiber-reinforced gypsum panels towhich the present invention relates from conventional prior art gypsumpanels, which are referred to as “wall board” or “dry wall” which haveat least one surface comprised of paper, including “wall board” or “drywall” having some form of fiber-reinforcement in the core.

The paperless gypsum/fiber board having improved impact resistance isproduced by embedding a reinforcing mesh, preferably a flexiblefiberglass mesh, in the back side of a multi-layer gypsum fiber board.In the process, the mesh is fed into the forming area of the panelbefore the panel is pressed prior to drying.

It is to be understood that the foregoing general description, and thefollowing detailed description, are exemplary and explanatory only andare not restrictive of the invention, as claimed.

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate several embodiments of theinvention and together with the description, serve to explain theoperation of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional end view of a homogeneous, one-layer board of thepresent invention;

FIG. 2 is a sectional end view of a multi-layer board of the presentinvention;

FIG. 3 is an illustration of a side view of a forming station of aproduction line in accordance with the present invention;

FIG. 3A is an illustration of a side view of a portion of a modifiedforming station of a production line in accordance with the presentinvention;

FIG. 4 is an illustration of a side view of a pressing area of aproduction line in accordance with the present invention; and

FIG. 5 is an illustration of a side view of a portion of anotherembodiment of the forming station of a production line in accordancewith the present invention.

FIG. 6 is a figure (FIG. 1) from U.S. Pat. No. 5,320,677 to Baig showinga schematic diagram of a process for forming a composite materialaccording to one aspect of the invention disclosed by U.S. Pat. No.5,320,677 to Baig.

FIG. 7 is a figure (FIG. 2) from U.S. Pat. No. 5,320,677 to Baig showinga schematic diagram of a process for forming a composite board accordingto another aspect of the invention disclosed by U.S. Pat. No. 5,320,677to Baig.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

The present invention relates generally to a paperless gypsum/fiberboard with improved impact resistance, and to a process for making sucha gypsum/fiber board. The paperless gypsum/fiber board having improvedimpact resistance is produced by embedding a reinforcing mesh,preferably a flexible fiberglass mesh, in the backside of a multi-layergypsum fiber board. In the process, the mesh is fed into the formingarea of the panel before the panel is pressed prior to drying.

The Mesh

Enhanced and improved impact resistance of the gypsum/fiber board isprovided by embedding a reinforcing mesh in the backside of thegypsum/fiber board. The mesh may be either woven or nonwoven and may bemade of a variety of materials. Preferably the mesh is made from a flatyarn of an inelastic material such as fiberglass mesh. Most preferablythe mesh is a fiber glass mesh having openings in the mesh of sufficientsize to allow a quantity of the dry gypsum/fiber mixture to pass throughthe mesh and embed the mesh in set gypsum in the final product.

One useful woven fiberglass mesh is available from Bayex under thenumber 0040/286. Bayex 0040/286 is a Leno weave mesh having a warp andweft of 6 per inch (ASTM D-3775), a weight of 4.5 ounces per square yard(ASTM D-3776), a thickness of 0.016 inches (ASTM D-1777) and a minimumtensile of 150 and 200 pounds per inch in the warp and weft,respectively (ASTM D-5035). It is alkali resistant and has a firm hand.Other fiberglass meshes having approximately the same dimensions haveopening of sufficient size to allow a portion of the gypsum/fiber mix topass through the mesh during formation of the board and may be used.

Another useful woven fiberglass mesh is available from Bayex under thenumber 0038/503. Bayex 0038/503 is a Leno weave mesh having a warp of 6per inch and weft of 5 per inch (ASTM D-3775), a weight of 4.2 ouncesper square yard (ASTM D-3776), a thickness of 0.016 inches (ASTM D-1777)and a minimum tensile of 150 and 165 pounds per inch in the warp andweft, respectively (ASTM D-5035). It is alkali resistant and has a firmhand.

Yet another useful woven fiberglass mesh is available from Bayex underthe number 0038/504. Bayex 0038/504 is a Leno weave mesh having a warpof 6 per inch and weft of 5 per inch (ASTM D-3775), a weight of 4.2ounces per square yard (ASTM D-3776), a thickness of 0.016 inches (ASTMD-1777) and a minimum tensile of 150 and 165 pounds per inch in the warpand weft, respectively (ASTM D-5035). It is alkali resistant and has afirm hand. Other fiberglass meshes having approximately the samedimensions have opening of sufficient size to allow a portion of thegypsum/fiber mix to pass through the mesh during formation of the boardand may be used.

Yet another useful woven fiberglass mesh is available from Bayex underthe number 4447/252. Bayex 4447/252 is a Leno weave mesh having a warpof 2.6 per inch and weft of 2.6 per inch (ASTM D-3775), a weight of 4.6ounces per square yard (ASTM D-3776), a thickness of 0.026 inches (ASTMD-1777) and a minimum tensile of 150 and 174 pounds per inch in the warpand weft, respectively (ASTM D-5035). It is alkali resistant and has afirm hand. Other fiberglass meshes having approximately the samedimensions have opening of sufficient size to allow a portion of thegypsum/fiber mix to pass through the mesh during formation of the boardand may be used.

The mesh is preferably embedded in the backside of the three-layer boardwith the warp oriented in the longitudinal direction of the board.Because the board of the present invention is expandedmulti-directionally during the pressing step, the use of a mesh which isextensible provides better bonding to the gypsum/fiber board.

It is preferred to have the mesh substantially embedded in the board andcovered by the gypsum/fiber mix, because this secures the mesh to theboard. Additionally, completely embedding the mesh in the gypsum/fibermix provides the best impact resistance to the board. Completelyembedding the mesh in the gypsum/fiber mix also makes the reinforcementless perceptible to the consumer.

Adhesives

In one embodiment, the mesh is treated with an adhesive in order toimprove the bond between the mesh and the gypsum/fiber board. Suitableadhesives include polyvinyl acetates, polyvinyl alcohols and proprietarytypes. Preferably the adhesive is water activated, i.e. activated due tomoistening by water of the board during the forming step of the boardmaking process.

The Gypsum/Fiber Board Composition

The materials used to produce the gypsum fiber board are conventionalmaterials. The term “gypsum”, as used herein, means calcium sulfate inthe stable dihydrate state; i.e. CaSO₄•2H₂O, and includes the naturallyoccurring mineral, the synthetically derived equivalents, such as FGDgypsum (a synthetic gypsum which is the by-product of flue gasdesulphurization), and the dihydrate material formed by the hydration ofcalcium sulfate hemihydrate (stucco) or anhydrite. The term “calciumsulfate material”, as used herein, means calcium sulfate in any of itsforms, namely calcium sulfate anhydrite, calcium sulfate hemihydrate,calcium sulfate dihydrate and mixtures thereof.

The fibers that serve to reinforce the gypsum are organic fibers, andare preferably cellulosic fibers that are readily available. For examplethe cellulosic fiber may be waste products such as waste paper, usednewspaper, inexpensive household waste paper, and reject fibers of pulpproduction.

Expanded perlite is used in the core of the product in order to reducethe density of the core layer. Conventional expanded perlite may beused. Preferably the perlite is expanded to a density range of about 5to 10 pounds per cubic foot range.

Additional components of the type conventionally used in gypsumfiberboard may be used in the board of the present invention. Suchconventional components include accelerators, wetting agents, fungicidesand the like.

Multi-Layer Gypsum Fiber Board

The present invention contemplates the formation of fiber-reinforcedgypsum panel having a homogeneous structure throughout, as illustratedby board 102 in FIG. 1, as well as composite boards having two or morelayers having distinct compositions 100 and 101 as illustrated in FIG.2. In board having a homogeneous structure, reinforcing mesh 120 isembedded in the back surface of the board as shown in FIG. 1. In boardhaving a multilayer structure, reinforcing mesh 120 may be positionedbetween the layers, e.g. between layers 100 and 101, but preferably themesh 120 is embedded in the back surface of outer layer 100 of the boardas shown in FIG. 2. The production line for making a multilayered board,having perlite and fiber and gypsum for the middle core, will first bedescribed. The use of the methods and equipment to produce differentboards according to the present invention will then be described.

The formation of the board can be described with reference to FIG. 3which shows three forming lines. Each forming line has three preformingbelts 3126, 3166 and 3136 on which the wetted fibers and dry calcinedgypsum with additives for the surface layers and wetted perlite, with orwithout fibers, and dry calcined gypsum for the core layer are formed.With reference to the top and bottom surface layers, wet fiber from themills (not shown) is carried by a closed loop pneumatic conveyor 2511,2512 to the forming station where the fibers are separated from the airby a cyclone. The separated fibers are deposited into shuttle conveyors3113 on the top of fiber formers 3114, 3134. The fiber formers spreadvia discharge rolls a preselected amount of fiber, according to theweight ratio of a preferred recipe, onto the preforming belts 3126,3136, forming a mat. Belt 3126 has a mat scale 3116.

Immediately downstream of the discharge rolls are scalper rolls 3117 and3137, respectively, which scrape off excess fiber and thereby equalizethe thickness of the mat. The scalper rolls can be adjusted in height toensure that the deposited mat of fibers has a uniform weight, and avacuum is applied at the rollers to pneumatically draw off excessfibers. Fibers scraped off by the scalper rolls are recycledpneumatically by pneumatic conveyors 2513 and 2507 into the same shuttleconveyors on the top of fiber formers 3114 and 3134. The preformingbelts operate at a constant speed.

The dry calcined gypsum additive mixture 2480 from distribution bin (notshown) is fed to plaster forming bins 3124, 3164, and 3144. The plaster,as explained below, is predominately calcined gypsum, although theplaster may include other conventional additives to control the chemicalprocess. The gypsum is metered from the forming bins by conventionalmeans, such as conveyors, chutes, or rollers. The bins have a variablespeed bottom belt conveyor with an integrated mat scale 3125, 3145, and3165 to control the amount of plaster deposited on the preforming beltdepending on the recipe. The correct amount of plaster is added as a toplayer onto the fiber mat. Elements 4911, 4913 and 4912 are permanentmagnets.

A continuous belt of mesh 120, which may be wound on supply roll 126, isfed onto forming belt 4010, as shown in FIG. 3. Preferably, the warp ofmesh 120 is oriented parallel to the direction of the movement offorming belt 4010.

At the head section 3146 of the preforming belts 3136, the fiber plasterlayer is guided downward onto mixing heads 3129, and 3148 and 3168. Themixing heads comprise sets of spike rollers (not shown) which thoroughlymix the fiber and plaster into a homogeneous composition and carry themixture from the head of the preforming belt (infeed) to the outfeed ofthe mixing head onto mesh 120 positioned on the forming belt 4010.Depending upon the distance from the preforming belt head to the mixinghead, a series of spike rolls controls the downward motion of thematerial. A portion of the fiber/plaster mix falls through the openingsof the reinforcing mesh 120 as the mesh moves on forming belt 4010.Spraying nozzles apply additional water to the bottom layer of the mat.

FIG. 3A illustrates an alternative embodiment in which mesh elevatingbar 128 is positioned between mesh 120 and forming belt 4010. Preferablybar 128 extends across the width of forming belt 4010. Bar 128 serves tospace mesh 120 about one inch above the surface forming belt 4010 asmesh 120 passes under mixing head 3129. The spacing of mesh 120 aboveforming belt 4010 allows a portion of the fiber/gypsum mixture fallingfrom mixture head 3129 to pass through the mesh to forming belt 4010 andembed the mesh, at least partially, in the finished board. If desired,bar 128 may be vibrated to cause a greater quantity of the gypsum/fibermixture to pass through mesh 120.

FIG. 5 illustrates another embodiment in which the mesh 120 passes undertensioning roller 136 and over placement roll 138 before it movesdownwardly toward forming belt 4010. Placement roll 138 serves to spacemesh 120 several inches above the surface forming belt 4010 as mesh 120passes under mixing head 3129. The spacing of mesh 120 above formingbelt 4010 allows a portion of the fiber/gypsum mixture falling frommixing head 3129 to pass through the mesh to forming belt 4010 and embedthe mesh, at least partially, in the finished board. The optimum spacingof mesh 120 above forming belt 4010 is dependent upon the size of theopenings in mesh 120, the moisture content of the fiber/gypsum mixture,the speed of forming belt 4010 and other process operating conditions.In the embodiment shown in FIG. 5, a spreading lip 140, that extendsacross the width of forming belt 4010, is attached to the outfeed sideof mixing head 3129. Spreading lip 140 serves to spread the mixture ofwefted fibers and gypsum across the width of the reinforcing mesh at apoint where mesh 120 is elevated above forming belt 4010. The embodimentshown in FIG. 5 allows an increased quantity of the fiber/gypsum mixtureto pass through the mesh to forming belt 4010 and produce a board inwhich the mesh is more completely embedded.

For a multilayered board, the core layer is formed in a similar mannerto that of the surface layer. In the example being described, a lowerpercentage of fiber is included in the core layer because a volume ofexpanded perlite is used in the core layer. Expanded perlite is includedin the core layer to reduce the overall specific weight of the board.The expanded perlite in combination with the gypsum provide a noncombustible core material which enables the core to pass the ASTM E136test procedure. Preferably, the mixture of wetted paper fibers andperlite particles are moisturized so that they will carry the waternecessary to hydrate the plaster to optimum strength added to form thecore layer. As explained below, in the preferred embodiment as adhesive,preferably liquid starch, is first mixed with the water for moisteningthe perlite, and the fibers are separately mixed with water. The wettedfibers and wetted perlite are then mixed together to form a uniformmixture.

Referring again to FIG. 3, a wetted perlite, starch and fiber mixture3152 (from conveyor not shown) is deposited in fiber former 3154, whichis identical in structure and operation to formers 3114, 3134. Theperlite, starch and fiber mixture is deposited onto preforming belt 3166through discharge rolls, in the same manner as the board surface layers.Preforming belt 3166 layers the perlite, starch and fiber mixture fromfiber former bin 3154 with the plaster from forming bin 3164 anddelivers the components to a mixing head 3168. Forming bin 3164 includesan integrated mat scale 3165. The core layer forming line includes ascalper roller 3157, mat scales 3156, and a mixing head 3168 thatoperate in the same manner as the elements in the surface forming line.

Following the formation of the mesh backed mat on the forming belt 4010,the three layered mat is pressed by a press line, shown in FIG. 4. Inone embodiment, the forming belt 4010 is also part of the press line andextends through the press and calibrating sections. In anotherembodiment (not shown), there is an open gap between the degassingstation and the compression station. Behind the last compressing rollerof the degassing station, spraying nozzles are installed for addingadditional water for moistening the top surface of the mat.

The press line includes three main sections, the degassing station 4012,the compression station 4013, and the calibration station 4014. Thesestations can be adjusted to vary the spacing between the conveyor beltsas well as the pressure being applied to the mat or gypsum, fibers,additives, and other materials. The adjustment of the station,therefore, allows the user to vary the thickness of the board.

Initially, the mat is pre-compressed by the degassing station 4012 toremove air from the mat. For a standard board, this station reduces themat from a thickness of several inches close to the final thickness thatcan vary, e.g. from ⅜ to ¾ inch. Taper belts are guided into this pressalong the outboard edges and center of the mat. The taper belts impart ataper into the pressed board along the edges of the panels. These tapersare beneficial for the taping and finishing of panels prior todecoration. Next, the degassed mat is pressed in compression station4013 where the mat is subject to a high load and pressed to the finalboard thickness. The mat then goes through calibration station section4014 which holds the thickness of the board to allow the setting processto continue.

After pressing and prior to drying, the boards are cut and prepared toenter the dryers. The boards, which are formed and pressed endlessly,are pre-trimmed and cut into e.g. 24 foot long pieces. High-pressurewater jets may be used to cut and trim the board. For example, 2stationary jets may be used to trim the sides, while a moving water jetcross cuts the board to length. While in the cutting area andimmediately prior to, the board is supported by a conveyor belt thatprovides forward motion. Alternatively, airjets or similar means (notshown) may provide an air cushion as is well known in the art. Beltconveyors (not shown in FIG. 4) accelerate the board to a high conveyingspeed.

Noncombustile Board

In a preferred embodiment, a three layer fiber-reinforced board isproduced with a core having a low content of organic materials thatallows the core to pass the ASTM E 136 test procedure. The improvedfiber-reinforced board of the present invention may be classified as noncombustible because the various code bodies, e.g. BOCA, provide for theremoval of ⅛″ from both the top and the bottom layers of the board priorto the application of the ASTM test procedure to core of the board. Withthe removal of the surface layers containing relatively high levels ofpaper fibers, the remaining portion, i.e. the core, becomesnon-combustible. Prior art fiberboards were relatively non-combustiblebecause they employ non-combustible fiber such as asbestos and mineralssuch as aluminum trihydrate that reduce the heat released during thetest. The board of the present invention passes the ASTM E136 testbecause the composition of the core contains a total of no more than 2%organic material, including a nominal 0.6% starch sprayed onto theperlite, with a paper content not exceeding 1.4% including paper fromclips (fiber) and paper from recycled panel materials. However the boardof the present invention has high strength that is provided by the highpaper fiber content in the surface layers.

In this embodiment, the composition of the three layers is shown belowin Table 1, including bottom surface layer (“SLB”), the top surfacelayer (“SLT”), and the center, core layer (“CL”).

TABLE 1 COMPONENT SLB SLT CL Dimension Paper Fiber 18 18 1.4 % Plaster82 82 62 % Perlite 0 0 36 % Starch 0 0 0.6 %

Reinforcement Process

The reinforcement process consists of laying out a fiberglass mesh overthe forming belt, spreading the bottom surface layer, consisting ofmixed paper fibers and plaster over the fiberglass mesh, followed by theapplication of additional water required for hydration. Once the surfacelayer/fiberglass mesh configuration has been established the core andtop layers are mixed, spread and deposited over the bottom surfacelayer. At this point, a 3-layer mat is formed and brought forward to theprecompressor where excess air is removed. Additional water required forhydration is added to the top surface layer and the mat is conveyedforward through the press. In the press the materials are compressed andthe plaster sets to bind all the materials together in the green /. Atthe same time the fiberglass mesh is embedded solidly into the bottomsurface of the green board.

The continuous green board exits the press, is cut to size with ahigh-pressure water-jet and individual panels are conveyed to the dryer.The free moisture after hydration is removed, the panels are conveyed tothe coating line where a sealant Is applied to the top surface of thepanels. The panels are then conveyed to a secondary dryer where excessmoisture is removed from the top surface of the panels. The panels areconveyed to the finishing line, cut-to-size, graded and packaged forshipping.

The following example will serve to illustrate the manufacture of agypsum/fiber board product within the present invention, that is a threelayer fiber-reinforced board produced with a core having a relativelylow content of organic material in order to be classified as anoncombustible building material as specified by various building codes(e.g. BOCA) and as tested according to ASTM E136. The board of thepresent invention achieves a noncombustible rating because thecomposition of the core contains a total of not more than about 2%organic materials, including a nominal 0.6% starch sprayed onto theperlite, and a paper content not exceeding 1.4% including paper fromclips (fiber) and paper from recycled panel materials. However, theboard of the present invention has high strength that is provided by thepaper fiber content in the surface layers. However, it should beunderstood that this example is set forth for illustrative purposes andthat many other gypsum fiber products are within the scope of thepresent invention.

EXAMPLE

Composite paperless fiber reinforced gypsum panels are produced in thefollowing manner. Calcined gypsum (calcium sulfate hemihydrate) isblended with recycled paper fibers, expanded perlite, starch, water andpotassium sulfate to form a three-layer board. Three formulations offiber and gypsum, shown below in Table 2, are prepared for use as thebottom surface layer (“SLB”), as the top surface layer (“SLT”), and asthe center layer (“CL”). These formulations are used to prepare a3-layer gypsum/fiber board ⅝ inches thick, using the continuous processand apparatus described above under the heading “MULTI-LAYER GYPSUMFIBER BOARD.”

TABLE 2 SLB SLT CL % % % Dry Dry Dry Part of Total Board % 28.0 28.0Component in Layer Fiber 18.0 18.0 1.4 Gypsum 82.0 82.0 61.4 Perlite 0 036.6 Starch 0 0 0.6 Dry Basis Total Layer 100 100 100 Water Wet BasisTotal Layer

The fiber used is a scrap paper fiber from magazines, newspapers andsimilar materials. The “plaster” is about 97% calcium sulfatehemihydrate, the balance being inert impurities. The plaster requiresabout 18% by weight of water to form the complete hydrate. Thereinforcing mesh was the Bayex 0038/503, described above.

The resulting three-layer board is ⅝ inches thick and has a density of55 pounds per cubic foot of which the center layer is 44% and thesurface layers 28% each. Owing to the relatively low paper content ofthe center layer, the resulting board may be classified as anoncombustible building material as specified by various building codes(e.g. BOCA). The improved fiber-reinforced board of the presentinvention achieves a noncombustible rating because the building codes(e.g. BOCA) allows the removal of ⅛″ from both the top and the bottomlayers of the board prior to combustion testing. With the removal of thesurface layers containing relatively high levels of paper fibers, theremaining portion, the core, is noncombustible when tested in accordancewith ASTM E136. Prior art fiberboards are relatively noncombustiblebecause they employ noncombustible fiber such as asbestos and mineralssuch as aluminum trihydrate, which reduces the heat released during thecombustion test. The board of the present invention achieves anoncombustible rating because the composition of the core contains atotal of not more than about 2% organic materials, including a nominal0.6% starch sprayed onto the perlite, and a paper content not exceeding1.4% including paper from clips (fiber) and paper from recycled panelmaterials. However, the board of the present invention has high strengththat is provided by the paper fiber content in the surface layers. Theboard had superior impact resistance, as shown by ASTM Test E-695,compared to similar board with no mesh reinforcement.

The board produced in the foregoing example was tested for impactresistance in accordance with the test method as prescribed under ASTME695. Several commercially available ⅝-inch thick boards were alsotested in accordance with ASTM E695. The results of the tests are shownbelow in Table 3.

TABLE 3 BOARD TYPE IMPACT STRENGTH (ft-lb) Type X gypsum board 120FIBEROCK AR 150 BOARD OF EXAMPLE >250

Type X gypsum board is a conventional gypsum wallboard. The FIBEROCK ARis a commercial product designated as Abuse Resistant that is producedwithout fiberglass mesh. The impact strength of the BOARD OF EXAMPLEexceeded the maximum limit of the apparatus on which it was tested.

The forms of invention shown and described herein are to be consideredonly as illustrative. It will be apparent to those skilled in the artthat numerous modifications may be made therein without departing fromthe spirit of the invention and the scope of the appended claims.

1. A method of producing a gypsum/fiber board having improved impactresistance, said method comprising the steps of: mixing predeterminedamounts of water and fibers, and dry calcined gypsum to form a mixtureof wetted, loose fibers and dry calcined gypsum; laying out areinforcing mesh over the upper surface of a forming belt; spacing saidmesh above said forming belt; depositing said mixture on said mesh toform a layer of said mixture, said layer of mixture having substantiallyuniform consistency; allowing a portion of said mixture to pass throughsaid mesh to said forming belt; adding additional water to said formedlayer; compressing said mesh together with said layer of mixture toembed said mesh in the lower surface of said layer and to form a boardcomposed of bonded fibers and gypsum with said mesh embedded in thesurface thereof; and drying said board to provide a finished board.
 2. Amethod of producing a gypsum/fiber board having improved impactresistance, said method comprising the steps of: mixing predeterminedamounts of fibers and water to form a mixture of wetted, loose fibers;mixing said wetted fibers with a predetermined amount of dry calcinedgypsum to form a mixed composition; laying out a reinforcing mesh overthe upper surface of a forming belt; spacing said mesh above saidforming belt; depositing said mixed composition on said mesh to form alayer of said mixed composition, said layer of mixed composition havingsubstantially uniform consistency; allowing a portion of said mixedcomposition to pass through said mesh to said forming belt; addingadditional water to said formed layer; compressing said mesh togetherwith said layer of mixed composition to embed said mesh in the lowersurface of said layer and to form a board composed of bonded fibers andgypsum with said mesh embedded in the surface thereof; and drying saidboard to provide a finished board.
 3. The method of claim 2, includingthe additional step of causing a portion of said mixed composition topass through the openings of said mesh prior to said compression step.4. The method of claim 2, wherein said mesh is vibrated across its widthat the point said mixed composition is deposited on said mesh.
 5. Themethod of claim 2, including the additional step of adding water to saiddeposited layer of mixed composition before said formed layer iscompressed.
 6. A method of producing a gypsum/fiber board havingimproved impact resistance, said method comprising the steps of: mixingpredetermined amounts of fibers and water to form a mixture of wetted,loose fibers; mixing said wetted fibers with a predetermined amount ofdry calcined gypsum to form a first composition; laying out areinforcing mesh over the upper surface of a forming belt; spacing saidmesh above said forming belt; depositing said first composition on saidmesh to form a layer of said first composition, said layer of firstcomposition having substantially uniform consistency; allowing a portionof said first composition to pass through said mesh to said formingbelt; adding additional water to said formed layer of said firstcomposition; mixing a low density porous particle mixture with water toform a supply of wetted low density particles; mixing said wetted lowdensity porous particles with a predetermined amount of dry calcinedgypsum to form a second composition; depositing said second compositionover said first layer to form a second layer having a substantialuniform consistency; mixing said wetted fibers with a predeterminedamount of dry calcined gypsum to form a third composition; depositingsaid third composition over said second layer to form a third layerhaving a substantial uniform consistency; and compressing said meshtogether with said three layers to embed said mesh in the surface ofsaid first layer and to form a board composed of bonded fibers andgypsum with said mesh embedded in the surface thereof; and drying saidboard to provide a finished board.
 7. The method of claim 6, includingthe additional step of causing a portion of said first composition topass through the openings of said mesh prior to said compression step.8. The method of claim 6, wherein said mesh is vibrated across its widthat the point said mixed composition is deposited on said mesh.
 9. Themethod of claim 6, including the additional step of adding water to saiddeposited layer of first composition before said deposited layer offirst composition is compressed.
 10. The method of claim 1, contacting asurface of the mesh with a bar or roll, over the forming belt, to spacethe mesh above the surface of the forming belt.
 11. The method of claim10, wherein the bar is a mesh elevating bar and the surface of the meshcontacts the mesh elevating bar, over the forming belt, to space themesh above the forming belt.
 12. A system for producing a gypsum/fiberboard having improved impact resistance, comprising: a roll ofreinforcing mesh having openings, a forming belt having an upper surfaceover which the mesh from the roll of reinforcing mesh is laid out; amixer for mixing wetted, loose fibers and dry calcined gypsum to form amixture of wetted, loose fibers and dry calcined gypsum and depositingsaid mixture on said mesh laid out over the upper surface of the formingbelt to form a layer of said mixture, said layer of mixture havingsubstantially uniform consistency, and to allow a portion of saidmixture to pass through the openings of said mesh to the forming belt;means for spacing the mesh above said forming belt; means for addingadditional water to said formed layer; a compressing station forcompressing said mesh together with said layer of mixture to embed saidmesh in the lower surface of said layer and to form a board composed ofbonded fibers and gypsum with said mesh embedded in the surface thereof;and a dryer downstream of the compressing station for drying said boardto provide a finished board.
 13. The system of claim 12, wherein saidmeans for spacing comprises a bar or roll for contacting a surface ofthe mesh, over the forming belt, to space the mesh above the surface ofthe forming belt.
 14. The system of claim 13, wherein said means forspacing comprises a mesh elevating bar for contacting the surface of themesh, over the forming belt, to space the mesh above the forming belt.15. The system of claim 14, wherein said mixer comprises a mixing headcomprising a spiked roll.
 16. The system of claim 12, wherein said mixercomprises a mixing head comprising a spiked roll.
 17. The system ofclaim 18, wherein said first mixer comprises a mixing head comprising aspiked roll.
 18. A system for producing a gypsum/fiber board havingimproved impact resistance, comprising: a roll of reinforcing meshhaving openings, a forming belt having an upper surface over which themesh from the roll of reinforcing mesh is laid out; a first mixer formixing wetted, loose fibers and dry calcined gypsum to form a firstcomposition of wetted, loose fibers and dry calcined gypsum anddepositing said first composition on said mesh laid out over the uppersurface of the forming belt to form a layer of said first composition,said layer of first composition having substantially uniformconsistency, and to allow a portion of said first composition to passthrough the openings of said mesh to the forming belt; means for spacingthe mesh above said forming belt; means for adding additional water tosaid formed layer of said first composition; means for mixing a lowdensity porous particle mixture with water to form a supply of wettedlow density particles; a second mixer for mixing wetted low densityporous particles, and dry calcined gypsum to form a second compositionand depositing said second composition over said first layer to form asecond layer having a substantial uniform consistency; a third mixer formixing wetted, loose fibers and dry calcined gypsum to form a thirdcomposition and depositing said third composition over said second layerto form a third layer having a substantial uniform consistency; meansfor compressing said mesh together with said three layers to embed saidmesh in the surface of said first layer and to form a board composed ofbonded fibers and gypsum with said mesh embedded in the surface thereof;and a dryer for drying said board to provide a finished board.
 19. Thesystem of claim 18, wherein said means for spacing comprises a bar orroll for contacting a surface of the mesh, over the forming belt, tospace the mesh above the surface of the forming belt.
 20. The system ofclaim 18, wherein said means spacing comprises a mesh elevating bar forcontacting the surface of the mesh, over the forming belt, to space themesh above the forming belt.